1. Field of the Invention
The present invention relates to a zoom lens assembly having a lens barrel capable of focusing and zooming through a single operating ring, and more particularly to a device for repetitive constant magnification photography using an improved zoom lens barrel.
2. Description of the Prior Art
Constant magnification photography may be achieved by adjusting the focus of the lens system in response to the change in the object distance and also by adjusting the focal length to correct for the change in magnification due to the change in the object distance. In the prior art, it is known to connect the zooming ring to the focusing ring in a predetermined manner so that a zooming operation, to off-set the change in magnification, may also automatically accompany the focusing operation to focus the system on a moving object.
Prior art devices for constant magnification photography can be broadly divided into two types. One type interlocks a focusing ring and a zooming ring of a zoom lens barrel with a correcting cam externally mounted on the zoom lens barrel to provide for relative rotation at a predetermined speed ratio. The other type electrically controls the rotating speed ratio of the focusing ring and the zooming ring. Both types utilize a zoom lens barrel which includes separate operating rings for focusing and zooming.
Japanese Patent Publication No. Sho 51-27577 published on Aug. 13, 1976 discloses a relatively compact zoom lens barrel capable of constant magnification photography. Cam grooves are disclosed for interconnecting a focusing operation ring with a zooming operation ring to provide constant magnification photography. This disclosure is not applicable to a zoom lens barrel having a single operational ring for both zooming and focusing.
Japanese Patent Laid Open Publication No. Sho 52-28875 published on March 15, 1977 discloses an electrical device for driving a zoom lens barrel of a single ring type to provide constant magnification photography. U.S. Pat. No. 4,083,057 and the Swiss Pat. No. 481,389 published on Dec. 31, 1969 are cited of general interest.
Achieving the advantages of constant magnification in a zoom lens system with a relatively simplified zoom lens barrel is still a goal sought to be achieved by the prior art particularly for application in 35 mm single lens reflex cameras.